This invention relates generally to turbine engines, and more particularly to methods and apparatus for reducing convection and aerodynamic bleed losses in turbine engines.
The efficiency of at least some known turbines is at least partially affected by the clearances defined between the rotating components and stationary components. Specifically, the magnitude of steady state clearances and transient radial clearances between the components may affect the turbine efficiency and/or operability margin. For example, a large transient clearance, or a clearance with significant variation around the circumference of the rotating component may adversely decrease the turbine efficiency and may result in engine stalls.
As described above, clearances may be affected by the rotor and the stator's transient thermal responses. Generally, known stators are built to be as lightweight as possible to meet engine weight metrics. This low stator weight makes the stator's transient thermal response typically faster than that of known rotors. Since the stator expands faster than the rotor, rotor tip clearances may increase transiently. Known stator assemblies include a plurality of stator rings coupled together. Specifically, such stator rings are coupled to each other with fasteners which extend through flanges, spaced about the outer circumference of the stator rings. To facilitate slowing the transient thermal response of the stator rings, at least some known turbine assemblies include U-shaped shields that cover the flanges. The shields accomplish this by reducing the convective film coefficients of the stator rings such that the stator rings experience a slower temperature-displacement response.
However, because such U-shaped shields are positioned adjacent the flowpath, the shields may adversely impact engine efficiency, specifically, such shields may increase aerodynamic losses associated with the compressor bleed flow. In some known compressors, aerodynamic losses are incurred because of windage, convection, and/or pressure losses due to the discharge of the air flow in a large cavity and the turbulence of the flow associated therewith.